Cancer can be viewed as a breakdown in the communication between tumor cells and their environment, including their normal neighboring cells. Signals, both growth-stimulatory and growth-inhibitory, are routinely exchanged between cells within a tissue. Normally, cells do not divide in the absence of stimulatory signals, and likewise, will cease dividing in the presence of inhibitory signals. In a cancerous, or neoplastic state, a cell acquires the ability to “override” these signals and to proliferate under conditions in which normal cells would not grow.
Cardiotonic steroids like digoxin and digitoxin are a class of naturally derived compounds that bind to and inhibit Na+/K+-ATPase (sodium pump). Members of this family have been used for the treatment of heart failure and arrhythmia for many years. Recent findings have revealed that these compounds may be involved in the regulation of several important cellular processes. Several cardiotonic steroids such as digitoxin and oleandrin have shown inhibitory effect on the growth of human tumor cells.